Fuel battery

ABSTRACT

There is provided a fuel cell having excellent portability and transportability and exhibiting superior power generation efficiency for which it is possible to use a liquid or solid fuel, which has higher energy density than a gaseous fuel. A fuel cell includes an electrolyte ( 1 ), an anode ( 2 ) and a cathode ( 3 ) that are disposed so as to sandwich the electrolyte ( 1 ), and further includes a fuel supply portion that supplies a fuel to the anode ( 2 ), an oxidant supply portion that supplies an oxidant containing oxygen to the cathode ( 3 ), and a cell heating portion that heats the fuel cell, and the electrolyte ( 1 ) is made of a solid oxide, and the fuel is a liquid or solid at room temperature and normal pressure.

TECHNICAL FIELD

The present invention relates to fuel cells.

BACKGROUND ART

Recently, various types of fuel cells, including those with largecapacities and those with small capacities, are being developed forspecific applications as clean power generating apparatuses that cancontribute to energy saving. In particular, utilizing their abilities tohave high capacities, fuel cells are expected to be commercialized aspower sources for mobile devices such as mobile phones and notebookcomputers to replace lithium ion batteries. The power sources for mobiledevices are required to have excellent portability and transportability.

In general, fuel cells are divided into several types depending on thetypes of the electrolyte used. In the case of a fuel cell (PEFC) thatuses a proton conductive polymer membrane (e.g., perfluoroethylenesulfonic acid, a typical example of which includes Nafion (R) by DuPont)as the electrolyte, the operating temperature is in the range from thevicinity of room temperature to about 100° C. On the other hand, in thecase of a fuel cell (SOFC) that uses an oxide ion conductive solidelectrolyte (e.g., zirconia-, ceria- or lanthanum gallate-basedceramics) as the electrolyte, the operating temperature is a hightemperature of 600° C. or above. These operating temperatures aredetermined by the characteristics of the electrolytes used for the fuelcells.

At present, extensive research is being carried out on PEFCs as portableand transportable fuel cells. PEFCs have an operating temperature closerto room temperature, and thus can save the use of heating devices.Furthermore, besides gaseous fuels such as hydrogen and natural gas,liquid fuels such as methanol can be used for fuel cells (fuel cellsusing methanol as the fuel may be referred to as DMFC, specifically).Liquid fuels have higher energy densities than gaseous fuels. Therefore,if liquid fuels can be used, then it is possible to provide a fuel cellhaving improved portability and transportability.

On the other hand, SOFCs have a high operating temperature of 600° C. orabove and thus require a heating device and a heat insulation structure,so that they are being developed mainly as stationary fuel cells, ratherthan as portable and transportable fuel cells. Therefore, gaseous fuels,such as hydrogen and natural gas, that continuously can be suppliedmainly are contemplated as the fuel used for SOFCs, and the structureand configuration of these fuel cells also are designed with the use ofgaseous fuels in mind.

In order to provide a fuel cell having excellent portability andtransportability, it is necessary to realize a fuel cell including asfew pieces of auxiliary equipment as possible, in addition to beingefficient and exhibiting high energy density. However, PEFCs, which usea polymer membrane as the electrolyte, require water management for thepolymer membrane due to their characteristics. For this purpose, it isnecessary to provide, for example, a humidification device forhumidifying air serving as an oxidant. When liquid fuels are used, thereis the possibility of permeation (cross-over) of the fuel through thepolymer membrane, resulting in decreased fuel utilization efficiency.Furthermore, since these fuel cells have a low operating temperature,they exhibit lower power generation efficiency and have a narrowerselection of fuels and catalysts, as compared with other types of fuelcells. In addition, when a gaseous fuel other than pure hydrogen isused, a reformer is required, so that separate energy is required forreforming the fuel.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a fuel cell havingexcellent portability and transportability for which it is possible touse a liquid or solid fuel, which has higher energy density than agaseous fuel.

A fuel cell according to the present invention includes an electrolyte;an anode and a cathode that are disposed so as to sandwich theelectrolyte; a fuel supply portion that supplies a fuel to the anode; anoxidant supply portion that supplies an oxidant containing oxygen to thecathode; and a cell heating portion that heats the fuel cell, whereinthe electrolyte is made of a solid oxide, and wherein the fuel is aliquid or solid at room temperature and normal pressure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an example of the fuel cellaccording to the present invention.

FIG. 2 is a schematic diagram showing another example of the fuel cellaccording to the present invention.

FIG. 3 is a schematic diagram showing an example of the cell heatingportion included in the fuel cell according to the present invention.

FIG. 4 is a schematic diagram showing another example of the cellheating portion included in the fuel cell according to the presentinvention.

FIG. 5 is a schematic diagram showing yet another example of the fuelcell according to the present invention.

FIG. 6 is a schematic diagram showing a still another example of thefuel cell according to the present invention.

FIG. 7 is a graph showing an example of the power generationcharacteristics of the fuel cell according to the present invention,measured in an embodiment.

FIG. 8 is a schematic diagram showing a further example of the fuel cellaccording to the present invention.

FIG. 9 is a graph showing an example of the power generationcharacteristics of the fuel cell according to the present invention,measured in an embodiment.

FIG. 10 is a graph showing an example of the power generationcharacteristics of the fuel cell according to the present invention,measured in an embodiment.

FIG. 11 is a schematic diagram showing a further example of the fuelcell according to the present invention.

FIG. 12 is a graph showing an example of the power generationcharacteristics of the fuel cell according to the present invention,measured in an embodiment.

FIG. 13 is a schematic diagram showing a further example of the fuelcell according to the present invention.

DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. It should be noted that in thefollowing description of the embodiments, the same reference numeralsmay be applied to the same members, and their overlapping descriptionsmay be omitted.

FIG. 1 shows an example of the fuel cell according to the presentinvention. The fuel cell shown in FIG. 1 is provided with an electrolyte1, as well as an anode 2 and a cathode 3 that are disposed so as tosandwich the electrolyte 1. Furthermore, it is provided with a quartztube 13 constituting a part of a fuel supply portion that supplies afuel to the anode 2, and a quartz tube 14 constituting a part of anoxidant supply portion that supplies an oxidant containing oxygen to thecathode 3. As shown in FIG. 1, the fuel is supplied to the anode 2through the quartz tube 13, and air, which is the oxidant, is suppliedto the cathode 3 through the quartz tube 14. Further, the fuel cellshown in FIG. 1 includes a heater 17 as a cell heating portion thatheats the fuel cell. The electrolyte 1 is made of a solid oxide, and thefuel is a liquid or solid at room temperature and normal pressure. Itshould be noted that in the present specification, “room temperature”refers to ambient temperature at which fuel cells usually are consideredto be used, including for example a temperature in the range from about−40° C. to about 50° C., and “normal pressure” refers to, for example, apressure in the rage from about 70 kPa to about 120 kPa.

In FIG. 1, the anode 2, the cathode 3, and the quartz tubes 13 and 14are housed inside alumina tubes 11. The alumina tubes 11 also serve asthe exhaust tube for discharging, for example, unreacted fuel oroxidant, and water produced by reaction. The alumina tubes 11 aredisposed on either the anode 2 side and the cathode 3 side, and arejoined with glass packing 12 with the electrolyte 1 disposedtherebetween. The glass packing 12 also serves to seal the anode 2 andthe cathode 3 from the outside.

By forming a fuel cell in the above described manner, it is possible toprovide a fuel cell having excellent portability and transportabilityand exhibiting superior power generation efficiency for which it ispossible to use a liquid or solid fuel, which has higher energyefficiency than a gaseous fuel.

It should be noted that hatching has been omitted in some portions ofFIG. 1 for the sake of clear explanation. The same also applies to therest of the drawings.

In the fuel cell of the present invention, there is no particularlimitation with respect to the electrolyte 1, as long as it is a solidoxide having oxide ion conductivity or proton conductivity.Particularly, a solid oxide having proton conductivity is preferable. Inthis case, the operating temperature can be lower than in the case ofusing a solid oxide having oxide ion conductivity, so that it ispossible to provide a fuel cell having more excellent portability andtransportability. It should be noted that “operating temperature” inthis specification refers to a temperature at which a fuel cell cangenerate power continuously. “Temperature” in “operating temperature”refers to the temperature of the electrolyte, for example.

There is no particular limitation with respect to the shape of theelectrolyte 1. For example, it may be planar or cylindrical. When theshape of the electrolyte 1 is planar, the thickness in a directionperpendicular to the principal surface may be in the range from 10 μm to500 μm, for example. When the thickness is too small, there is thepossibility of a cross leak of the fuel or the oxidant from the anode tothe cathode (from the cathode to the anode). When the thickness is toolarge, on the other hand, there is the possibility of decreased ionicconductivity, which reduces the performance as the cell.

In the fuel cell of the present invention, the electrolyte 1 may containbarium (Ba) and at least one selected from cerium (Ce) and zirconium(Zr). Such an electrolyte has excellent proton conductivity, so that itis possible to provide a fuel cell exhibiting even higher powergeneration efficiency.

In the fuel cell of the present invention, the electrolyte may have acomposition ratio represented by the formula:Ba(Zr_(1-x)Ce_(x))_(1-y)M_(y)Al_(z)O_(3-α) wherein M is at least oneselected from In and trivalent rare-earth elements excluding Ce. Thatis, M is at least one selected from Gd, Y, Yb, Sm and In. Further, x, y,z and a are numerical values that satisfy, respectively, therelationships: 0≦x≦1, 0<y<0.4, 0≦z<0.04, and 0<α<1.5. Such anelectrolyte has excellent proton conductivity, so that it is possible toprovide a fuel cell exhibiting even higher power generation efficiency.It should be noted that α is a numerical value representing the degreeof oxygen loss in the electrolyte, and this also applies to theelectrolytes described below.

In particular, it is preferable that the above-described M is at leastone selected from In, Gd, Y and Yb. More specifically, the electrolytemay have a composition ratio represented by at least one selected fromthe formulae: BaCe_(0.8)Gd_(0.2)Al_(0.2)O_(3-α),BaZr_(0.6)Ce_(0.2)Gd_(0.2)O_(3-α) and BaZr_(0.4)Ce_(0.4)In_(0.2)O_(3-α),for example. Such an electrolyte has excellent proton conductivity, sothat it is possible to provide a fuel cell exhibiting even higher powergeneration efficiency.

Besides the above, it is possible to use, for example,La_(0.8)Sr_(0.2)Ga_(0.8)Mg_(0.15)Co_(0.05)O_(3-α),La_(0.8)Sr_(0.2)Ga_(0.8)Mg_(0.15)Fe_(0.05)O_(3-α) orLa_(0.8)Sr_(0.2)Ga_(0.8)Mg_(0.2)O_(3-α) as the electrolyte 1.

In the fuel cell of the present invention, there is no particularlimitation with respect to, for example, the shape or composition of theanode 2, as long as the supplied fuel can be oxidized. For example, itis sufficient that the anode includes a catalyst (anode catalyst)containing at least one selected from Pt, Ni, Ru, Ir and Pd. Inparticular, when a catalyst containing Pt is used, a highly efficientfuel cell can be provided.

In the fuel cell of the present invention, there is no particularlimitation with respect to, for example, the shape or composition of thecathode 3, as long as oxygen can be reduced. For example, it issufficient that the cathode includes a catalyst (cathode catalyst)containing Pt, for example, as a composition.

Here, an exemplary method for forming the anode 2 and the cathode 3 willbe described. The anode 2 and the cathode 3 may be formed, for example,by applying a paint containing the above-described anode catalyst ontoone principal surface of the electrolyte 1 and applying a paintcontaining the above-described cathode catalyst onto the other principalsurface. After application, each of the catalysts is dried or baked,thereby obtaining a laminate in which the anode 2 and the cathode 3 areformed on either principal surface of the electrolyte. With this method,the shapes of the anode 2 and the cathode 3 can be determined by theshape of the electrolyte.

The thus formed laminate further is sandwiched by a pair of separatorsserving both as a fuel or oxidant channel and a current collector, thusforming a fuel cell in which the separator, the anode, the electrolyte,the cathode and the separator are laminated in this order (this stategenerally is called “single cell”). At this time, when the electrolyteand the separators are planar, a planar fuel cell can be obtained.Furthermore, a plurality of the above-described single cells may bestacked to form a stack. Since the single cells are connectedelectrically to each other in series, the overall output voltage of thefuel cell can be increased by increasing the number of the single cellsto be stacked. Additionally, a flat plate made of, for example, metal,such as stainless steel, or carbon may be used as the separators.Further, the electrolyte onto which the anode and the cathode are formedmay be sandwiched by a pair of the separators in such a manner that theanode or the cathode is in contact with a surface on which the fuel oroxidant channel is formed of the separators. FIG. 2 shows an example ofa planar fuel cell including such separators.

In the fuel cell shown in FIG. 2, a laminate 4 that is constituted by ananode, an electrolyte and a cathode is held on a substrate 5 made ofceramic. Four pieces of the laminates 4 are held on the substrate 5, andportions of the anode and the cathode of each of the laminates 4 areexposed to the outside from openings that are formed in the substrate 5.The fuel and the oxidant are supplied to these exposed portions. Inaddition, the substrate 5 and the laminates 4 are sandwiched by a pairof separators 18 serving both as a fuel or oxidant channel and a currentcollector. A fuel supply tube 20 and an anode exhaust tube 22, or anoxidant supply tube 21 and a cathode exhaust tube 23, are connected tothe separators 18. The separators 18 further are sandwiched by thin-filmheaters 19, and the entire cell can be heated with the heaters 19.Furthermore, the entire fuel cell is covered with a heat insulatingmaterial 24.

Alternatively, the fuel cell also can be constructed by disposing alaminate formed as above in a housing in which an anode chamber and acathode chamber are formed, such that the anode faces the anode chamberand the cathode faces the cathode chamber (that is, the anode chamberand the cathode chamber are separated from each other by the laminate).In this case, the fuel may be supplied to the anode chamber, and theoxidant may be supplied to the cathode chamber. In addition, there is noparticular limitation with respect to, for example, the material forforming the anode chamber and the cathode chamber, and the capacity orshape of the anode chamber and the cathode chamber. Further, the fuelcell can be constructed by disposing a laminate formed as above inside ahousing in such a manner that the interior of the housing is dividedinto at least two regions. In this case, the fuel may be supplied to theregion that the anode of the laminate faces, and the oxidant may besupplied to the region that the cathode of the laminate faces. Inaddition, there is no particular limitation with respect to, forexample, the material of the housing, and the capacity or shape of eachof the regions.

In the fuel cell of the present invention, there is no particularlimitation with respect to, for example, the configuration or mechanismof the fuel supply portion, as long as the fuel can be supplied to theanode. For example, the fuel supply portion may be configured using atank or cartridge that stores the fuel, or a pump or the fuel supplytube that delivers the fuel to the anode. In addition, since the fuelcell according to the present invention uses a fuel that is a liquid orsolid at room temperature and normal pressure, the size and the weightof the tank, the pump and the like can be made smaller than in the caseof fuel cells using, for example, a high pressure gas or liquidhydrogen. Accordingly, it is possible to provide a fuel cell havingexcellent portability and transportability.

There is no particular limitation with respect to, for example, theconfiguration or mechanism of the oxidant supply portion, as long as theoxidant can be supplied to the cathode. For example, the oxidant supplyportion may be configured using a tank or cartridge that stores theoxidant, or a pump, a compressor or the oxidant supply tube thatdelivers the oxidant to the cathode. There is no particular limitationwith respect to the oxidant, as long as it contains oxygen, and air maybe used, for example. When air is used as the oxidant, the tank or thelike that stores the oxidant can be omitted. Further, when the oxidantcan be used at the atmospheric pressure, the pump, compressor or thelike also can be omitted.

There is no particular limitation with respect to, for example, theconfiguration or mechanism of the cell heating portion, as long as thecell can be heated. For example, the cell heating portion may beconfigured using a heater. In particular, the use of a thin-film heater19 as shown in FIG. 2 allows the heater to have a smaller capacity andto be arranged more freely, thus providing a fuel cell having even moreexcellent portability and transportability. The shape of the heaterreadily can be changed to match the shape of the portion where theheater is disposed. There is no particular limitation with respect tothe shape of the thin-film heater 19. For example, as shown in FIG. 3,it is possible to use a heater 19 in which a heating element 31 thatgenerates heat when it is supplied with electric current is disposed ina thin-film structure 33 having heat conductivity. The electric currentmay be applied to the heating element 31 via terminals 32, for example.Any material capable of being formed as a thin film and having somedegree of heat conductivity may be used as the material for thestructure 33, without any particular limitation. For example, it ispossible to use mica or ceramic (e.g., silica or alumina). There is noparticular limitation with respect to the material used for the heatingelement 31, and it is possible to use stainless steel, nichrome orplatinum, for example. It should be noted that FIG. 3 shows an exampleof the simplest configuration for the thin-film heater 19. Whenrequired, a plurality of heating elements 31 having different propertiesmay be included. Furthermore, it is possible to use a heater 19 in whichthe surface in contact with a member that is desired to be heated isconstituted by the structure 33 having heat conductivity and a heatinsulating material is disposed on the opposite surface.

A thin-film heater 19 as shown in FIG. 3 can be used regardless ofwhether the fuel cell is planar or cylindrical. When the fuel cell iscylindrical, the cell heating portion may have a configuration in whichthe heating element 31 simply is wound around a cylindrical electrodeplate. FIG. 4 shows an example of such a cell heating portion. In theexample shown in FIG. 4, as the cell heating portion, the heatingelement 31 is wound around a cylindrical anode 2 (in which anelectrolyte and a cathode are disposed). The cell can be heated byapplying electric current to the heating element 31. Thus, in the fuelcell of the present invention, for example, the configuration or shapeof the cell heating portion may be set freely.

The cell heating portion may heat any member of the cell, as necessary.For example, it may heat the separators, as described above, or may heatthe electrodes such as the anode and the cathode. It also may heat thefuel supply portion or the oxidant supply portion. It may heat the fuelitself. When the fuel is a solid fuel, it is preferable to heat the fuelitself. An example in which the fuel itself is heated will be describedlater in the embodiments.

In the fuel cell of the present invention, the cell heating portion mayinclude a catalyst for reacting the fuel with the oxidant. In this case,the cell can be heated by supplying portions of the fuel and the oxidantto the catalyst, so that it is possible to provide a fuel cell of higherefficiency than when the cell heating portion includes a heater (in thecase of using a heater, power for the heater is required). FIG. 5 showsan example of such a fuel cell.

In the fuel cell shown in FIG. 5, catalytic layers 30 are disposed so asto be in contact with the separators 18. Each of the catalytic layers 30is disposed on one of the separators 18 on the surface that is oppositefrom the surface facing the anode 2 or the cathode 3. Furthermore, thefuel cell has a configuration that permits a gas mixture (the fuel-airgas mixture in FIG. 5) of unreacted fuel that is exhausted withoutreacting in the anode 2 and unreacted oxidant that is exhausted withoutreacting in the cathode 3 to be supplied to the catalytic layers 30.Accordingly, in the fuel cell shown in FIG. 5, it is possible to mixunused fuel of the fuel supplied from a tank 42, which constitutes apart of the fuel supply portion, and unused air of the air supplied froma compressor 27, which constitutes a part of the oxidant supply portion,after they are discharged from the separators 18, and to react themusing the catalytic layers 30. Heat resulting from the reaction can beused to increase or to maintain the cell temperature. Furthermore, theamount of heat generated in the catalytic layers 30 can be controlled byadjusting the flow rates of the fuel and the oxidant.

There is no particular limitation with respect to the catalyst forreacting the fuel with the oxidant, and it is possible to use Pt, Pd, Rhor Ru, for example. The catalyst may be applied onto the separators ofthe cell, for example, in the form of a paste. Alternatively, a chamberfilled with the catalyst may be formed, and this chamber may be disposedso as to be in contact with the cell.

There is no particular limitation with respect to the method forsupplying the fuel and the oxidant to the catalyst. For example,portions of the fuel and the oxidant may be separated to be supplied tothe catalyst, before the fuel and the oxidant are supplied to the anodeand the cathode. In this case, by disposing a valve at a branchingpoint, it is possible to supply the fuel and the oxidant to the catalystonly when necessary.

Furthermore, as shown in FIG. 5, unused fuel and oxidant that areexhausted from the anode and the cathode may be supplied to thecatalyst. In a fuel cell, all the fuel and the oxidant that are suppliedto the anode and the cathode cannot always be consumed at the anode andthe cathode (the ratio of the actually consumed amount to the suppliedamount is referred to as a “utilization rate”). In general, immediatelyafter startup, at which the cell temperature is low, the utilizationrate is low, resulting in a large amount of unused fuel and oxidant.Furthermore, since the cell temperature is low, it is more necessary toheat the cell immediately after startup than at any other time.Therefore, by supplying unused fuel and oxidant to the catalyst, it ispossible to provide a fuel cell of even higher efficiency.

There is no particular limitation with respect to the position at whichthe catalytic layers 30 are disposed. In the example shown in FIG. 5,the catalytic layers 30 are disposed so as to be in contact with theseparators 18. However, the catalytic layers 30 may be disposed at anygiven position, as long as heat generated in the catalytic layers 30 canbe conducted to a member that is desired to be heated. When necessary,an optional material may be disposed between the catalytic layers 30 anda member that is desired to be heated. Furthermore, there also is noparticular limitation with respect to the shape of the above-describedcatalyst, and the catalyst may be formed as layers as shown in FIG. 5,or as a block or a porous structure. Alternatively, the above-describedcatalyst may be attached and carried on the surface of a porous productsuch as a filter. It should be noted that although FIG. 5 shows anexample of the planar fuel cell, it is possible to provide a fuel cellof even higher efficiency, by disposing the catalytic layers 30 in acylindrical fuel cell in a similar manner. For example, the catalyticlayers 30 may be disposed as shown in FIG. 6. FIG. 6 shows an example ofa so-called cylindrical Tammann tube type fuel cell, in which thecatalytic layers 30 are disposed on the surface of the inner wall of anexhaust tube serving as both the anode exhaust tube and the cathodeexhaust tube.

The fuel cell according to the present invention further may include acollection portion (cathode collection portion) that collects, fromexhaust of the cathode, at least one selected from the oxidant and waterthat are contained in the exhaust. By collecting water, it is possibleto obtain water from the fuel cell, and also to reuse the collectedwater as the fuel. There is no particular limitation with respect to,for example, the mechanism or configuration of the cathode collectionportion. For example, the oxidant and/or water in the form of liquid canbe collected by using a gas-liquid separating device in a state in whichthe temperature of the cathode exhaust is 100° C. or lower. A specificexample of such a fuel cell will be described later in the embodiments.

Furthermore, the fuel cell according to the present invention mayinclude a collection portion (anode collection portion) that collects,from exhaust of the anode, at least one selected from the fuel, carbondioxide and water that are contained in the exhaust. By collecting thefuel, it is possible to reuse unused fuel, thus providing a fuel cellhaving even more excellent portability and transportability. Bycollecting water, it is possible to obtain water from the fuel cell, andalso to reuse the collected water as the fuel. Moreover, by collectingcarbon dioxide, it is possible to use the cell in a closed space. Bycollecting carbon dioxide separately from the fuel at this time, it ispossible to prevent a gas that does not contribute to power generationfrom being mixed into the fuel that is to be reused. There is noparticular limitation with respect to, for example, the mechanism orconfiguration of the anode collection portion. For example, it ispossible to collect carbon dioxide, which is a gas, by using agas-liquid separating device.

In other words, in the fuel cell according to the present invention, thefuel supply portion further may include a fuel circulation portion thatresupplies unused fuel contained in exhaust of the anode to the anode.Furthermore, the fuel circulation portion may include a carbon dioxidecollection portion that collects carbon dioxide contained in the anodeexhaust. There is no particular limitation with respect to, for example,the mechanism or configuration of the carbon dioxide collection portion.For example, it is possible to use the above-described gas-liquidseparating device, or a chamber filled with a basic solid such as sodiumhydroxide. Further, there is no particular limitation with respect to,for example, the mechanism or configuration of the fuel circulationportion. A specific example of such a fuel cell will be described laterin the embodiments.

In the fuel cell of the present invention, there is no particularlimitation with respect to the fuel, as long as it is a liquid or solidat room temperature and normal pressure. As described above, “roomtemperature” means a temperature, for example, in the range from about−40° C. to about 50° C., preferably in the range from −20° C. to 40° C.“Normal pressure” means a pressure, for example, in the range from about70 kPa to about 120 kPa. A temperature in the above-described rangescorresponds to ambient temperature at which human beings presumably canperform activities (that is, the fuel cell of the present inventiongenerally is used). The fuel need not be a liquid or solid in all theabove-described ranges. It may be a liquid or solid in some of theabove-described ranges. It may be in a mixed state of a liquid and asolid. For example, butane has a boiling point of −0.5° C., and is a gasat 20° C. and a pressure of 1 atmosphere. However, it turns into aliquid at −0.5° C. or below, and easily is liquefied even at 20° C. withonly a slight pressure applied. Therefore, it can be included as thefuel used for the fuel cell of the present invention. Additionally,butane is commercially available in large quantities as a small andlight portable cylinder gas.

More specifically, the fuel may be a mixture of an organic fuel andwater, for example. There is no particular limitation with respect tothe organic fuel, as long as it can be mixed with water. For example,the fuel may be at least one selected from methanol, ethanol, propanol,butanol and dimethyl ether. These lower alcohols can be mixed with waterreadily, and at any given ratio. In particular, it is preferable to useat least one selected from ethanol, propanol, butanol and dimethylether. These organic fuels do not have toxicity, unlike methanol, sothat it is possible to provide a fuel cell offering a higher level ofsafety.

In the fuel cell of the present invention, the fuel may be at least oneselected from methanol, ethanol, propanol, butanol, trioxane,dimethoxymethane, dimethyl ether, butane and trimethoxymethane. Inparticular, it is preferable to use at least one selected from ethanol,propanol, butanol, butane and dimethyl ether. These fuels do not havetoxicity, unlike methanol, so it is possible to provide a fuel celloffering a higher level of safety.

In the fuel cell of the present invention, the fuel may be a solid atroom temperature and normal pressure. For example, it may be a higheraliphatic alcohol having about 12 to about 26 carbon atoms. Morespecifically, the fuel may be at least one selected from dodecanol and1-tetradecanol. It should be noted that dodecanol and 1-tetradecanol donot have toxicity, unlike methanol.

Furthermore, the fuel may be, for example, gasoline, kerosene, light oilor heavy oil. Each of these may be a fuel that is commercially availableas gasoline, kerosene, light oil or heavy oil. Although commerciallyavailable gasoline contains various additives mixed therein, “gasoline”generally refers to a fuel having a lowest boiling fraction of about 30°C. to about 220° C. when refined from crude oil and containinghydrocarbons having about 4 to about 12 carbon atoms. For example, itcorresponds to the fuels defined in JIS (Japanese IndustrialStandard)-K-2201, JIS-K-2202 and JIS-K-2206. “Kerosene” generally refersto a fuel made of fractions having a boiling point in the range fromabout 145° C. to about 300° C. For example, it corresponds to the fueldefined in JIS-K-2203. “Light oil” generally refers to a fuel made offractions having a boiling point in the range from about 180° C. toabout 350° C. For example, it corresponds to the fuel defined inJIS-K-2204. “Heavy oil” is a fuel containing, as a component, residualoil that remains after refining, for example, gasoline, kerosene andlight oil from crude oil, and corresponds to, for example, the fueldefined in JIS-K-2205.

Alternatively, the fuel may be an alcohol-containing gel. Specificexamples include a solid fuel that is a gel formed by mixing alcoholwith a saturated solution of calcium acetate.

In the above-described fuel cell of the present invention, the operatingtemperature may be, for example, in the range from 100° C. to 500° C.,more preferably in the range from 150° C. to 350° C. These ranges arehigher than the operating temperature range of PEFCs, so that it ispossible to provide a fuel cell exhibiting higher power generationefficiency than that of PEFCs. Furthermore, these ranges are lower thanthe operating temperature of SOFCs, so that it is possible to provide afuel cell that enables simplification of the heating device and the heatinsulation device as compared with SOFCs and that has excellentportability and transportability, which have been difficult to achievefor SOFCs.

EMBODIMENTS

Hereinafter, the present invention will be described in further detailby way of embodiments. It should be noted that the present invention isnot limited to the following embodiments.

Embodiment 1

In this embodiment, a fuel cell was produced actually, and powergeneration tests were carried out using, as the fuel, methanol, ethanol,propyl alcohol, butyl alcohol, methanol mixed with water (with a watercontent of 50 wt %), each of which was a liquid at room temperature andnormal pressure, and butane. First, the method for producing the fuelcell used in this embodiment will be described.

First, an oxide having proton conductivity (in the shape of a 13 mmφdisk with a thickness of 220 μm) was produced as an electrolyte. Morespecifically, a columnar sintered product of the above-described oxide(13 mmφ, 10 mm thick) was formed by a high temperature solid-phaseprocess, and this was subjected to cutting and polishing, therebyproducing an electrolyte with a thickness of 220 μm. In addition, theelectrolyte (oxide) had the composition:BaZr_(0.4)Ce_(0.4)In_(0.2)O_(3-α) (wherein 0<α<0.3).

Next, a platinum paste (manufactured by Tanaka Kikinzoku Group, modelnumber: TR7905) was applied as a catalyst onto both sides of the thusproduced disk electrolyte, and baking was performed to form an anode anda cathode. Each of the anode and the cathode has a thickness of about 5μm.

Then, the thus formed laminate of the anode, the electrolyte and thecathode was used to produce a fuel cell shown in FIG. 1. As describedabove, in the fuel cell shown in FIG. 1, the anode 2 and the cathode 3are formed on either side of the electrolyte 1, and the electrolyte 1 issandwiched by the alumina tubes 11 via the glass packing 12. The fuel issupplied to the anode 2 through the quartz tube 13, and air, which isthe oxidant, is supplied to the cathode 3 through the quartz tube 14.The quartz tube 13 and the quartz tube 14 constitute a part of the fuelsupply portion and that of the oxidant supply portion, respectively.Furthermore, an output lead wire 15 and a potential measuring lead wire16 are bonded to each of the anode 2 and the cathode 3, so that it ispossible to measure the voltage generated between the anode 2 and thecathode 3 (cell voltage), while outputting electric power generated bypower generation to the outside. In the fuel cell shown in FIG. 1, asthe cell heating portion, the heater 17 further is disposed so as tocover the alumina tubes 11. The alumina tubes 11 are one type of theabove-described housing.

Power generation tests were conducted on the thus produced fuel cell.The test method will be described below. First, the interior of thealumina tubes 11 was heated to 350° C. with the heater 17. At this time,the temperatures of the electrolyte 1, the anode 2 and the cathode 3were set to 350° C. (such a state is referred to a cell temperaturebeing 350° C.). Next, the fuel and the air were supplied through thequartz tube 13 and the quartz tube 14, and the relationship between thecurrent density, which was the load, and the cell voltage (I-Vcharacteristics) was measured. The results of the I-V characteristicsare shown in FIG. 7.

As shown in FIG. 7, it was found that power generation was possible ineach of the cases in which methanol, ethanol, propanol, butanol,methanol mixed with water, and butane were used as the fuel.Furthermore, results that were substantially the same as those shown inFIG. 7 also could be obtained when the cell temperature was 100° C.,150° C. or 200° C.

Furthermore, substantially the same results also could be obtained whenother oxides having proton conductivity, including, for example,BaZr_(0.6)Ce_(0.2)Gd_(0.2)O_(3-α), BaZr_(0.4)Ce_(0.4)Y_(0.2)O_(3-α),BaZr_(0.4)Ce_(0.4)Yb_(0.2)O_(3-α), BaCe_(0.8)Gd_(0.2)O_(3-α),BaCe_(0.5)Gd_(0.2)Al_(0.2)O_(3-α),BaZr_(0.4)Ce_(0.4)In_(0.2)Al_(0.2)O_(3-α),BaZr_(0.6)Ce_(0.2)Gd_(0.2)In_(0.2)O_(3-α),BaZr_(0.52)Ce_(0.24)Gd_(0.24)O_(3-α),BaZr_(0.56)Ce_(0.24)Gd_(0.2)O_(3-α), BaZr_(0.3)Ce_(0.5)In_(0.2)O_(3-α)(however, in all of the above-described composition formulae, 0<α<0.3)were used as the oxide used for the electrolyte.

In addition, substantially the same results also could be obtained whena catalyst containing Ru or Rh was used as the catalyst used for theanode and the cathode, and when the thickness of the electrolyte was inthe range from 10 μm to 500 μm.

Embodiment 2

In this embodiment, a fuel cell is produced actually, and powergeneration tests were carried out using methanol mixed with water (witha water content of 50 wt %) as the fuel. First, the method for producingthe fuel cell used in this embodiment will be described.

First, an oxide having proton conductivity (in the shape of a 13 mmφdisk with a thickness of 220 μm) was produced as an electrolyte. Morespecifically, a columnar sintered product of the above-described oxide(13 mmφ, 10 mm thick) was formed by a high temperature solid-phaseprocess, and this was subjected to cutting and polishing, therebyproducing an electrolyte with a thickness of 220 μm. In addition, theelectrolyte (oxide) had the composition:BaCe_(0.8)Gd_(0.2)Al_(0.02)O_(3-α) (wherein 0<α<0.3).

Next, a platinum paste (manufactured by Tanaka Kikinzoku Group, modelnumber: TR7905) was applied as a catalyst onto both sides of the thusproduced disk electrolyte, and baking was performed to form an anode anda cathode. Each of the anode and the cathode has a thickness of about 2μm.

Then, the thus formed laminate of the anode, the electrolyte and thecathode was used to produce a fuel cell shown in FIG. 2. As describedabove, in the fuel cell shown in FIG. 2, the laminate 4 constituted bythe anode, the electrolyte and the cathode is held on the substrate 5made of ceramic. Four pieces of the laminates 4 are held on thesubstrate 5, and portions of the anode and the cathode of each of thelaminates 4 are exposed to the outside from openings that are formed inthe substrate 5. Since the fuel and the oxidant are supplied to theseexposed portions, the electrode area of the fuel cell shown in FIG. 2 isequal to the total area of the exposed portions. In this embodiment, thetotal electrode area was 2 cm².

Further, in the fuel cell shown in FIG. 2, the substrate 5 and thelaminates 4 are sandwiched by a pair of the separators 18 serving asboth a fuel or oxidant channel and a current collector. The fuel supplytube 20 and the anode exhaust tube 22, or the oxidant supply tube 21 andthe cathode exhaust tube 23, are connected to the separators 18. Theseparators 1& further are sandwiched by the thin-film heaters 19, andthe entire cell can be heated with the heaters 19. Furthermore, theentire fuel cell shown in FIG. 2 is covered with the heat insulatingmaterial 24 made of a material containing silica. In addition, stainlesssteel was used as the material of the separators 18.

FIG. 8 shows a schematic diagram of the entire fuel cell shown in FIG.2. As shown in FIG. 8, the fuel cell shown in FIG. 2 is provided with asecondary battery as an auxiliary power source 29, and can supplyelectric power from the auxiliary power source 29 to the heaters 19 atthe startup of the cell. Accordingly, it is possible to heat thelaminates 4, each constituted by the anode 2, the electrolyte 1 and thecathode 3, to a predetermined temperature using the electric power fromthe auxiliary power source 29, and then to supply the fuel and the air,which is the oxidant, to generate power. After the start of powergeneration, once the cell temperature can be maintained by heatgenerated during power generation, supply of electric power from theauxiliary power source 29 to the heater 19 may be suspended, and,conversely, the auxiliary power source 29 may be charged with thegenerated electric power.

Furthermore, the fuel cell shown in FIG. 2 is provided with the tank 26and the pump 25 (with an output of 0.15 mW) as the fuel supply portion,as shown in FIG. 8. The tank 26 is connected also to the anode exhausttube 22, and also serves as the anode collection portion and the fuelcirculation portion. Moreover, the tank 26 includes a gas-liquidseparating device, and thus can exhaust only carbon dioxide contained inthe anode exhaust to the outside. In addition, a piezoelectric pump wasused as the pump 25.

Similarly, the fuel cell shown in FIG. 2 is provided with the compressor27 as the oxidant supply portion, and the tank 28 as the cathodecollection portion. The tank 28 includes a gas-liquid separating device,and can exhaust only the air contained in the cathode exhaust to theoutside.

Power generation tests were carried out on the thus produced fuel cellusing methanol mixed with water (with a water content of 50 wt %) as thefuel. At this time, the cell temperature was set to 350° C., and therelationship between the load current and the cell voltage (the I-Vcharacteristics in FIG. 9) and the relationship between the load currentand the output (the output characteristics in FIG. 9) were evaluated.The results are shown in FIG. 9. In FIG. 9, the horizontal axis denotesthe load current (mA).

As shown in FIG. 9, in this embodiment, a maximum output of 1 mW couldbe obtained. At this time, after subtracting the power consumed by theauxiliary machinery such as the pump, the heater and the compressor, anoutput of about 0.15 mW still could be obtained. That is, it was foundthat the fuel cell of this embodiment was capable of independent powergeneration, covering the auxiliary machinery. Therefore, it can be saidthat the fuel cell of this embodiment is a fuel cell having excellentportability and transportability.

In addition, substantially the same results also could be obtained whenthe electrolytes described in Embodiment 1 were used as the electrolyte.Further, substantially the same results could be obtained when acatalyst containing Ru or Rh was used as the catalyst used for the anodeand the cathode, and when the thickness of the electrolyte was in therange from 10 μm to 500 μm. Moreover, the output could be improved evenfurther when a material with a lower electric resistance was used as thematerial of the separator.

Embodiment 3

In this embodiment, a fuel cell in which the configuration of the fuelcell shown in FIG. 2 was modified partially was produced, and powergeneration tests were performed.

First, an oxide having proton conductivity (in the shape of a 13 mmφdisk with a thickness of 220 μm) was produced as an electrolyte. Morespecifically, a columnar sintered product of the above-described oxide(13 mmφ, 10 mm thick) was formed by a high temperature solid-phaseprocess, and this was subjected to cutting and polishing, therebyproducing an electrolyte with a thickness of 220 μm. In addition, theelectrolyte (oxide) had the composition:BaZr_(0.6)Ce_(0.2)Gd_(0.2)O_(3-α) (wherein 0<α<0.3).

Next, a platinum paste (manufactured by Tanaka Kikinzoku Group, modelnumber: TR7905) was applied as a catalyst onto both sides of the thusproduced disk electrolyte, and baking was performed to produce an anodeand a cathode. Each of the anode and the cathode has a thickness ofabout 3 μm.

Then, the thus formed laminate of the anode, the electrolyte and thecathode was used to produce a fuel cell shown in FIG. 2. However, inthis embodiment, catalytic layers containing Pt were disposed as thecatalyst for reacting the fuel with the oxidant, in place of the heaters19. Furthermore, carbon was used as the material of the separators 18.FIG. 5 shows a schematic diagram of the entire fuel cell used in thisembodiment (the rest of the configuration, the electrode area and othersare the same as those in Embodiment 2).

As described above, in the fuel cell of this embodiment, the catalyticlayers 30 are disposed so as to be in contact with the separators 18. Insuch a fuel cell, it is possible to mix unused fuel of the fuel suppliedfrom the tank 42, which constitutes the fuel supply portion, and unusedair of the air supplied from the compressor 27, which constitutes theoxidant supply portion, after they are discharged from the separators18, and to react them using the catalytic layers 30. Heat resulting fromthe reaction can be used to increase or to maintain the celltemperature. Furthermore, the amount of heat generated in the catalyticlayers 30 can be controlled by adjusting the flow rates of the fuel andthe oxidant. In addition, the area of the catalytic layers 30 was set tobe the same as that of the separators 18, and the thickness of thecatalytic layer 30 was set to 5 μm.

Power generation tests were carried out on the thus produced fuel cellusing butane as the fuel. First, butane and air were supplied to andburned in the catalytic layers 30 to set the cell temperature to about350° C. Next, the flow rates of butane and the air were adjusted, andpower generation tests were performed. The results are shown in FIG. 10.

As shown in FIG. 10, in this embodiment, a maximum output of 0.35 mWcould be obtained. At this time, after subtracting the power consumed bythe auxiliary machinery such as the pump, an output of about 0.2 mWstill could be obtained. That is, it was found that the fuel cell ofthis embodiment was capable of independent power generation, coveringthe auxiliary machinery. Therefore, it can be said that the fuel cell ofthis emulsion is a fuel cell having excellent portability andtransportability.

In addition, substantially the same results also could be obtained whenthe electrolytes described in Embodiment 1 were used as the electrolyte.Substantially the same results also could be obtained when the anodecollection portion and/or the cathode collection portion was disposed.Further, substantially the same results also could be obtained when acatalyst containing Ru or Rh was used as the catalyst used for the anodeand the cathode, and when the thickness of the electrolyte was in therange from 10 μm to 500 μm.

Embodiment 4

In this embodiment, a fuel cell in which the configuration of the fuelcell shown in FIG. 1 was modified partially was produced, and powergeneration tests were performed. Furthermore, fuels that are solids atroom temperature and normal pressure (an alcohol-containing gel,dodecanol and 1-tetradecanol) were used as the fuel.

First, an oxide having proton conductivity (in the shape of a 13 mmφdisk with a thickness of 220 μm) was produced as an electrolyte. Morespecifically, a columnar sintered product of the above-described oxide(13 mmφ, 10 mm thick) was formed by a high temperature solid-phaseprocess, and this was subjected to cutting and polishing, therebyproducing an electrolyte with a thickness of 220 μm. In addition, theelectrolyte (oxide) had the composition:BaZr_(0.4)Ce_(0.4)In_(0.2)Al_(0.01)O_(3-α) (wherein 0<α<0.3).

Next, a platinum paste (manufactured by Tanaka Kikinzoku Group, modelnumber: TR7905) was applied as a catalyst onto both sides of the thusproduced disk electrolyte, and baking was performed to produce an anodeand a cathode. Each of the anode and the cathode has a thickness ofabout 8 μm.

Then, the thus formed laminate of the anode, the electrolyte and thecathode was used to produce a fuel cell shown in FIG. 11. The fuel cellshown in FIG. 11 is identical to the fuel cell shown in FIG. 1, exceptthat a tank 41 in which a solid fuel is sealed is embedded in the heater17. Since the tank 41 is embedded in the heater 17, the fuel cell shownin FIG. 11 is a fuel cell capable of heating the fuel with the cellheating portion.

Power generation tests were performed on the thus produced fuel cell,with the cell temperature being set to 350° C. It should be noted thatthe alcohol-containing gel used as the fuel is a solid fuel that is agel formed by mixing ethanol with a saturated solution of calciumacetate. The results of the power generation tests are shown in FIG. 12.

As shown in FIG. 12, it was found that sufficient power generation alsowas possible in the cases of using, as the fuel, dodecanol,1-tetradecanol and the alcohol-containing gel, which were solids at roomtemperature and normal pressure.

In addition, substantially the same results also could be obtained whenthe electrolytes described in Embodiment 1 were used as the electrolyte.Further, substantially the same results could be obtained when acatalyst containing Ru or Rh was used as the catalyst used for the anodeand the cathode, and when the thickness of the electrolyte was in therange from 10 μm to 500 μm.

Embodiment 5

In this embodiment, an example will be described in which a prototype ofa fuel cell that was intended for power sources used for personalcomputers (PCs), mobile phones and the like was produced actually. FIG.13 shows a fuel cell 51 that was contemplated in this embodiment. Thefuel cell 51 shown in FIG. 13 includes: a cell 52; a fuel tank 57; apump 54 that supplies the fuel from the fuel tank 57 to the cell 52; ananode collection portion 53; a compressor 55 that supplies air to thecell 52; and a cathode collection portion 56. A laminate of theelectrolyte 1, the anode 2, the cathode 3, the separators 18 and thecatalytic layers 30, as shown in FIG. 5, was used as the cell 52. Inaddition, the size of the fuel cell 51 was 30 mm×30 mm×20 mm, and theelectrode area of the cell 52 was 3 cm².

It was found that in the case of using the oxides described above inEmbodiments 1 to 4 as the electrolyte, the catalysts described above inEmbodiments 1 to 4 as the anode and the cathode, and the fuels describedabove in Embodiments 1 to 4 as the fuel for the thus produced fuel cell,it was possible to provide a fuel cell having higher energy conversionefficiency and an actual capacity that was about 1.2 time larger than aPEFC having an equivalent size, including the auxiliary machinery. Thecapacity was calculated from the obtained I-V curve (current-voltagecharacteristics curve).

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, it is possibleto provide a fuel cell having excellent portability and transportabilityand exhibiting superior power generation efficiency for which it ispossible to use a liquid or solid fuel, which has higher energy densitythan a gaseous fuel.

1. A fuel cell comprising: an electrolyte; an anode and a cathode thatare disposed so as to sandwich the electrolyte; a fuel supply portionthat supplies a fuel to the anode; an oxidant supply portion thatsupplies an oxidant containing oxygen to the cathode; and a cell heatingportion that heats the fuel cell, wherein the electrolyte is made of asolid oxide; and the fuel is a liquid or solid at room temperature andnormal pressure.
 2. The fuel cell according to claim 1, furthercomprising: a collection portion that collects, from exhaust of thecathode, at least one selected from the oxidant and water that arecontained in the exhaust.
 3. The fuel cell according to claim 1, furthercomprising: a collection portion that collects, from exhaust of theanode, at least one selected from the fuel, carbon dioxide and waterthat are contained in the exhaust.
 4. The fuel cell according to claim1, wherein the fuel supply portion includes a fuel circulation portionthat resupplies unused fuel contained in exhaust of the anode to theanode.
 5. The fuel cell according to claim 4, wherein the fuelcirculation portion further includes a carbon dioxide collection portionthat collects carbon dioxide contained in the exhaust.
 6. The fuel cellaccording to claim 1, wherein the cell heating portion includes acatalyst for reacting the fuel with the oxidant.
 7. The fuel cellaccording to claim 6, wherein the fuel and the oxidant contain,respectively, unused fuel and oxidant that are exhausted from the anodeand the cathode.
 8. The fuel cell according to claim 1, wherein theelectrolyte is made of an oxide having proton conductivity.
 9. The fuelcell according to claim 8, wherein the electrolyte contains barium (Ba)and at least one selected from cerium (Ce) and zirconium (Zr).
 10. Thefuel cell according to claim 9, wherein the electrolyte has acomposition ratio represented by a formula:Ba(Zr_(1-x)Ce_(x))_(1-y)M_(y)A_(z)O_(3-α); wherein M is at least oneselected from In and trivalent rare-earth elements excluding Ce; andwherein x, y, z and a are numerical values that satisfy, respectively,the following relationships: 0≦x≦1 0<y≦0.4 0≦z<0.04 0<a<1.5.
 11. Thefuel cell according to claim 10, wherein the M is at least one selectedfrom In, Gd, Y and Yb.
 12. The fuel cell according to claim 11, whereinthe electrolyte has a composition represented by at least one selectedfrom formulae: BaCe_(0.8)Gd_(0.2)Al_(0.02)O_(3-α),BaZr_(0.6)Ce_(0.2)Gd_(0.2)O_(3-α) and BaZr_(0.4)Ce_(0.4)In_(0.2)O_(3-α).13. The fuel cell according to claim 1, wherein the fuel is a mixture ofan organic fuel and water.
 14. The fuel cell according to claim 13,wherein the organic fuel is at least one selected from methanol,ethanol, propanol, butanol and dimethyl ether.
 15. The fuel cellaccording to claim 14, wherein the organic fuel is at least one selectedfrom ethanol, propanol, butanol and dimethyl ether.
 16. The fuel cellaccording to claim 1, wherein the fuel is at least one selected frommethanol, ethanol, propanol, butanol, trioxane, dimethoxymethane,trimethoxymethane, dodecanol, dimethyl ether, butane and 1-tetradecanol.17. The fuel cell according to claim 16, wherein the fuel is at leastone selected from ethanol, propanol, butanol, dodecanol, dimethyl ether,butane and 1-tetradecanol.
 18. The fuel cell according to claim 1,wherein the fuel is a higher aliphatic alcohol having at least 12 and atmost 26 carbon atoms.
 19. The fuel cell according to claim 1, whereinthe fuel is at least one selected from gasoline, kerosene, light oil andheavy oil.
 20. The fuel cell according to claim 1, wherein the fuel isan alcohol-containing gel.
 21. The fuel cell according to claim 1,wherein an operating temperature is in the range from 100° C. to 500° C.